Wow, lots of mixed opinions here. I think The Hurt Locker was over rated, it was really boring and weak, terrible story, etc. I don't know how it won best picture... or how critics liked it.
I liked Up in the Air a lot, even after seeing it 3 times.
Both Up in the Air and The Hurt Locker were "Like it or Hate it" movies though, so I think the fair winner should have been Avatar.